The present invention relates to a damper assembly for damping the amplitude of vibrations of a rotating shaft and particularly relates to a damper assembly employing brush bristles to provide the damping action.
Dampers for supporting the bearings on a rotating shaft are also well known. For example, squeeze film bearing dampers are often used. Fundamentally a squeeze film damper comprises a centering spring that holds either a ball bearing or a tilting pad bearing about the rotating shaft. An oil film under pressure is disposed between the centering spring and a fixed support. The damping action is generated by the orbital motion of the outer race or centering spring which squeezes the oil film. In an alternative squeeze-type damper design, another way of generating the damping action is to use an annular solid damping insert, for example, an insert formed of metal mesh, between the fixed support and the damper centering spring.
It is also well known that rotating shafts in turbines and generators are prone to vibrations and dynamic loads caused by rotor or shaft imbalances. Most types of bearings in such systems, however, provide very little damping to the system. In applications of this type, it is necessary to have a moderate amount of damping in the system to traverse the critical speeds with low amplitude of motion and to maintain the rotor system stable. That is, in a system which has negligible damping, such as a system employing ball bearings, the system passes through one or more resonant frequencies as the system moves toward its operating speed. Consequently, damping of the system is required during startup and shutdown to avoid adverse effects on the system at resonant frequencies.
In accordance with a preferred embodiment of the present invention, there is provided a damping system for the bearing of a rotating shaft wherein the damping action is provided by a brush having brush bristles disposed in an annular array about the bearing. As employed in a damping system hereof, the brush bristles are disposed between a fixed support and a centering spring (movable support) carrying the bearing about the shaft. It will be appreciated that the centering spring and fixed support do not rotate about the shaft axis. The movable support, however, moves radially and orbitally in response to radial excursions of the shaft, including vibration. The bristles absorb the radial and orbital displacements of the centering spring.
In a preferred form of the present invention, a pair of annular arrays of brush bristles are spaced axially one from the other defining a cavity therebetween. While the damping action is obtained through the interaction of the bristles and their engagement at their tips with the centering spring, which dissipates the vibrational energy of the shaft, the magnitude of the damping action can be controlled by pressurizing the cavity between the arrays of brush seals. By pressurizing the cavity, the bristles are displaced axially and increase their damping force on the centering spring. The bristles, in effect, extend along their axis such that the tips exert a substantial and elastic radially inward force on the centering spring and hence moderate pressures within the cavity.
In a preferred embodiment according to the present invention, there is provided a damper assembly comprising a shaft having an axis of rotation, a bearing about the shaft, a fixed component about the bearing, a non-rotatable, radially and orbitally movable support carrying the bearing and carried by the fixed component and a generally annular damping element interposed between the fixed component and the support, the element including a generally annular array of brush bristles extending in a generally radial plane from the fixed component with tips thereof in engagement with the support to diminish the amplitude of the shaft vibrations.
In a further preferred embodiment according to the present invention, there is provided in a damper assembly including a bearing about a rotatable shaft, a fixed component about the bearing, a non-rotatable radially and orbitally movable support carrying the bearing and carried by the fixed component, a method of damping shaft vibrations including the steps of disposing a damping element between the fixed component and the support having a generally annular array of bristles, and engaging tips of the bristles against the support to diminish the amplitude of shaft vibrations.